1. Field of the Invention
The present invention relates to a lead storage type pencil, known as a mechanical pencil, and more particularly to a so-called mechanical pencil as a carpenter's pencil.
2. Description of the Prior Art
A carpenter's pencil is peculiar in that it has a wide flat lead core, generally of rectangular cross-section, encased in a flat wooden casing. Such a pencil is more robust than a cylindrical round pencil, for use in the field, and is more useful for providing a straight line mark on a board with a carpenter's square.
Although there are any number of mechanical pencils to substitute for a round, cylindrical type pencil, there are no known commercial mechanical pencils to replace the wood-and-lead type carpenter's pencil. The prior art mechanical pencil mechanisms are generally adapted to circular cylindrical lead bits and are not easily adaptable to flat, wide rectangular bits.
U.S. Pat. No. 1,766,271, issued June 24, 1930 to H. Turner, is directed to a flat lead bit within a circular cylindrical casing with a mechanism, such as a coil spring, which requires a circular cylindrical configuration. This patent utilizes a pair of flat clamp plates as clutches for holding the lead bit in place.
There is, however, a lipstick holder, described in U.S. Pat. No. 2,043,250, issued June 9, 1936 to N. Kasdan et al, which proposes to contain and extend a lipstick of rectangular cross-section. The lipstick holder in the Kasdan et al holder includes a sliding carrier, and a spring detent cooperates with teeth on the inside of a casing and the carrier to engage the teeth at a given position. This patent does provide a mechanism which could be adapted to a mechanical carpenter's pencil. With a mechanical carpenter's pencil, however, certain problems would still exist.
It is important that the construction of the casing be as slim as possible in order that the feel to the user is similar to that of a conventional carpenter's pencil, yet the inner walls of the casing should be spaced from the lead bit so as not to break the otherwise brittle lead bit. Since it is intended that the casing be of molded plastics material, it will necessarily be at least slightly flexible, in view of the dimensions thereof. Furthermore, there exists a problem in holding the lead bit in the casing, in view of the brittleness of the lead bit, which is not contemplated in the Kasdan et al patent in view of the relative softness of lipstick.